OFFSET LITHO PRINTING
Offset litho printing allows the greatest flexibility of ink colours and stock types and is always the best option when a large number of copies of the same original are required.
Offset litho works on the principle that oil and water don’t mix. A flexible printing plate made of aluminium or polyester is used. Water is absorbed in the non image areas which repels the ink, the ink adheres to the image area. This image is transferred to a rubber blanket, this mirror image is then applied to the sheet.
Due to the fact that a litho printed job has setting up costs: the making of a film and plate, the mixing of an ink and the make ready of the machine etc; the unit cost of a few copies is quite high. However, once the initial set up is covered, litho is fast, high quality and economical.
Litho is very flexible in the stocks it can run. From a 60gsm bank sheet through to a 400gsm board, in coated or uncoated stock.
ARTWORK CONSIDERATIONS
The main considerations when preparing artwork for litho printing are resolution and colour. Litho plates are prepared at a very high resolution and are therefore capable of producing a very high quality sharp results. It is important to run through our checklist carefully and make sure that resolutions and image types are the best possible. Please take a couple of minutes to familiarise yourself with the various colour options below if you are not used to preparing artwork.
SINGLE COLOUR/GREYSCALE
The simplest and cheapest litho option. This single colour need not be black! A colour chart of almost 1,000 colours in produced by pantone. Standard tin colours are available at no extra charge, special mixes do incur a small charge.
Reproduction of photographs, greyscale images and graduated tints are excellent when using litho. When producing artwork it is often easiest to produce the job in black and then specify when ordering which pantone colour you would like us to produce the job in.
SPOT COLOUR
For 2 and 3 colour offset print jobs or jobs requiring an exact colour match not achievable using CMYK, spot colour are used. Each colour ink has its own plate.
Producing artwork for spot colour printing is probably the trickiest. It is important that your design package allows spot colour separation.
Please be sure to look at our checklist and if in doubt – ASK!
FULL COLOUR PRINTING
Also referred to as CMYK or four colour process. This is how 90% of the printed matter you will see is produced.
Through using cyan, magenta, yellow and black transparent inks it is possible to produce full colour reproduction. There are limitations, particular ends of colour sphere are not possible to achieve, specific oranges and greens sometimes cause problems. However, for the majority of colour reproduction this is satisfactory. A separate pantone chart giving recipes in CMYK percentages is available. When a very specific shade is required which is not achievable using CMYK it is sometimes necessary to run a fifth plate, CMYK + spot.
Most good design packages are suitable for producing CMYK artwork. Please be careful to have a look at our checklist before submitting this type of artwork. Because of the relatively high costs involved it is important that everything is correct!